High molecular weight poly(2,6-dimethyl-1,4-phenylene ether) and process therefor

ABSTRACT

A poly(2,6-dimethyl-1,4-phenylene ether) having a high molecular weight and a reduced content of low molecular weight species can be prepared by a method that includes specific conditions for the oxidative polymerization, chelation, and isolation steps. The poly(2,6-dimethyl-1,4-phenylene ether) is particularly useful for the fabrication of fluid separation membranes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.12/255,694, filed Oct. 22, 2008, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/030,336, filed Feb. 21, 2008.The related applications are fully incorporated herein by reference.

BACKGROUND OF THE INVENTION

Polyphenylene ether) resin is a type of plastic known for its excellentwater resistance, dimensional stability, and inherent flame retardancy,as well as high oxygen permeability and oxygen/nitrogen selectivity.Properties such as strength, stiffness, chemical resistance, and heatresistance can be tailored by blending it with various other plastics inorder to meet the requirements of a wide variety of consumer products,for example, plumbing fixtures, electrical boxes, automotive parts, andinsulation for wire and cable.

The most commercially important polyphenylene ether is currentlypoly(2,6-dimethyl-1,4-phenylene ether), which is prepared on a largescale by the oxidative polymerization of 2,6-dimethylphenol (also knownas 2,6-xylenol). For certain product applications, notably use in hollowfiber membranes, very high molecular weightpoly(2,6-dimethyl-1,4-phenylene ether)s are needed. Not only must theaverage molecular weight be very high, but the sample must have a smallweight percent of low molecular weight polymer chains. There istherefore a need for poly(2,6-dimethyl-1,4-phenylene ether)s that havebut a high number average molecular weight and a reduced fraction of lowmolecular weight molecules.

The literature includes various procedures for the preparation of highmolecular weight poly(2,6-dimethyl-1,4-phenylene ether)s, but theseprocedures are deficient for one reason or another. For example, U.S.Pat. Nos. 4,110,311 and 4,116,939 to Cooper et al. require the additionof chemical compounds that interfere with the solvent recycling that isrequired to make commercial process environmentally acceptable.Specifically, U.S. Pat. No. 4,110,311 requires the addition of adihydric phenol and a mild reducing during the copper removal step, andU.S. Pat. No. 4,116,939 requires the addition of an aromatic amine. Asanother example, U.S. Pat. No. 6,472,499 B1 to Braat et al. provides acommercially viable process for producing high molecular weightpoly(2,6-dimethyl-1,4-phenylene ether)s, but the present inventors haveobserved that the products of the Braat et al. process, once isolated,have a relatively large fraction of lower molecular weight molecules.Other references provide procedures that are suitable for use on alaboratory scale, but for reasons that are not always well understood itis difficult or impossible to successfully translate the procedures to acommercial scale. It should also be noted that many referencescharacterize product poly(2,6-dimethyl-1,4-phenylene ether)s in terms ofintrinsic viscosity, rather than molecular weight, and there is no wayto deduce a specific molecular weight distribution from an intrinsicviscosity value.

There therefore remains a need for poly(2,6-dimethyl-1,4-phenyleneether)s having high number average molecular weight and reduced contentof molecules with low molecular weight (e.g., polymer chains with amolecular weight less than 30,000 atomic mass units). There is also aneed for improved, commercially scalable, and environmentally acceptableprocesses for producing such poly(2,6-dimethyl-1,4-phenylene ether)s.

BRIEF DESCRIPTION OF THE INVENTION

The above-described and other drawbacks are alleviated by a method ofpreparing a high molecular weight poly(2,6-dimethyl-1,4-phenyleneether), comprising: oxidatively polymerizing 2,6-dimethylphenol intoluene solvent in the presence of a catalyst comprising copper ion andN,N′-di-tert-butylethylenediamine to form a reaction mixture comprisinga dissolved poly(2,6-dimethyl-1,4-phenylene ether), water, and thecatalyst; wherein the oxidative polymerizing comprises initiatingoxidative polymerization in the presence of no more than 10 weightpercent of the 2,6-dimethylphenol; wherein at least 95 weight percent ofthe 2,6-dimethylphenol is added to the reaction mixture after theinitiation of oxidative polymerization and over the course of at least50 minutes; wherein the oxidatively polymerizing comprises addingmolecular oxygen and 2,6-dimethylphenol to the reaction mixture in amole ratio of 0.3:1 to 0.65:1; terminating the oxidative polymerizationto form a post-termination reaction mixture; combining a chelantcomprising an alkali metal salt of nitrilotriacetic acid with thepost-termination reaction mixture to form a chelation mixture comprisingan aqueous phase comprising chelated copper ion and an organic phasecomprising the dissolved poly(2,6-dimethyl-1,4-phenylene ether); whereinthe chelation mixture excludes dihydric phenols and aromatic amines;maintaining the chelation mixture at a temperature of 40 to 55° C. for 5to 100 minutes; separating the aqueous phase and the organic phase;wherein the separation is conducted at a temperature of 40 to 55° C.;and isolating the poly(2,6-dimethyl-1,4-phenylene ether) from theseparated organic phase; wherein time elapsed between termination of theoxidative polymerization and isolating thepoly(2,6-dimethyl-1,4-phenylene ether) is no more than 200 minutes; andwherein the isolated poly(2,6-dimethyl-1,4-phenylene ether) has a numberaverage molecular weight of at least 18,000 atomic mass units and lessthan 30 weight percent of molecules having a molecular weight less than30,000 atomic mass units.

Another embodiment is a poly(2,6-dimethyl-1,4-phenylene ether) solidhaving a number average molecular weight of at least 18,000 atomic massunits, and less than 30 weight percent of molecules having a molecularweight less than 30,000 atomic mass units.

Another embodiment is a fiber comprising thepoly(2,6-dimethyl-1,4-phenylene ether) solid.

Another embodiment is an article comprising thepoly(2,6-dimethyl-1,4-phenylene ether) solid.

Another embodiment is an asymmetric hollow fiber membrane comprising thepoly(2,6-dimethyl-1,4-phenylene ether) solid.

Another embodiment is a fluid separation apparatus comprising theasymmetric hollow fiber membrane.

These and other embodiments are described in detail below.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, when practicing the poly(2,6-dimethyl-1,4-phenyleneether) synthesis method of U.S. Pat. No. 6,472,499 B1 to Braat et al. ona commercial scale, the present inventors observed that the finallyisolated poly(2,6-dimethyl-1,4-phenylene ether) had a relatively largefraction of lower molecular weight molecules, despite its high weightaverage molecular weight. Through extensive research on the process, theinventors arrived at a very specific combination of process conditionsthat is effective to produce a poly(2,6-dimethyl-1,4-phenylene ether)having both a high number average molecular weight and a low fraction oflow molecular weight molecules. Thus, one embodiment is a method ofpreparing a high molecular weight poly(2,6-dimethyl-1,4-phenyleneether), comprising: oxidatively polymerizing 2,6-dimethylphenol intoluene solvent in the presence of a catalyst comprising copper ion andN,N′-di-tert-butylethylenediamine to form a reaction mixture comprisinga dissolved poly(2,6-dimethyl-1,4-phenylene ether), water, and thecatalyst; wherein the oxidative polymerizing comprises initiatingoxidative polymerization in the presence of no more than 10 weightpercent of the 2,6-dimethylphenol (wherein at least 95 weight percent ofthe 2,6-dimethylphenol is added to the reaction mixture after theinitiation of oxidative polymerization and over the course of at least50 minutes, and wherein the oxidatively polymerizing comprises addingmolecular oxygen and 2,6-dimethylphenol to the reaction mixture in amole ratio of 0.3:1 to 0.65:1); terminating the oxidative polymerizationto form a post-termination reaction mixture; combining a chelantcomprising an alkali metal salt of nitrilotriacetic acid with thepost-termination reaction mixture to form a chelation mixture comprisingan aqueous phase comprising chelated copper ion and an organic phasecomprising the dissolved poly(2,6-dimethyl-1,4-phenylene ether) (whereinthe chelation mixture excludes dihydric phenols and aromatic amines);maintaining the chelation mixture at a temperature of 40 to 55° C. for 5to 100 minutes; separating the aqueous phase and the organic phase;wherein the separation is conducted at a temperature of 40 to 55° C.;and isolating the poly(2,6-dimethyl-1,4-phenylene ether) from theseparated organic phase; wherein time elapsed between termination of theoxidative polymerization and isolating thepoly(2,6-dimethyl-1,4-phenylene ether) is no more than 200 minutes; andwherein the isolated poly(2,6-dimethyl-1,4-phenylene ether) has a numberaverage molecular weight of at least 18,000 atomic mass units and lessthan 30 weight percent of molecules having a molecular weight less than30,000 atomic mass units. Several aspects of this process aresurprising. First, it was unexpected that the intrinsic viscosity dropobserved between termination of the polymerization reaction andisolation of the final product could be substantially reduced withoutadding to the chelation mixture the dihydric phenol and mild reducingrequired by U.S. Pat. No. 4,110,311, or the aromatic amine required byU.S. Pat. No. 4,116,939. Second, it was unexpected that the time andtemperature of the chelation step could be substantially reduced withoutinterfering with the copper recovery that is the primary purpose of thatstep. Third, it was unexpected that the intrinsic viscosity drop couldbe reduced by maintaining a particular fixed addition ratio of molecularoxygen to 2,6-dimethylphenol (rather than using the conventionaltechnique of regulating oxygen addition to maintain a constantconcentration of oxygen in the reactor headspace). Fourth, it wasunexpected that the process could produce an isolatedpoly(2,6-dimethyl-1,4-phenylene ether) having a number average molecularweight of at least 18,000 atomic mass units and less than 30 weightpercent of molecules having a molecular weight less than 30,000 atomicmass units. Fifth, it was unexpected that a pre-concentration (solventremoval) step could be excluded from the process without adverselyaffecting isolation of the poly(2,6-dimethyl-1,4-phenylene ether).

The process includes the step of oxidatively polymerizing2,6-dimethylphenol. The oxidative polymerization is conducted in toluenesolvent in the presence of a catalyst comprising copper ion andN,N′-di-tert-butylethylenediamine to form a reaction mixture comprisinga dissolved poly(2,6-dimethyl-1,4-phenylene ether), water, and thecatalyst. In some embodiments, the catalyst further comprisesdimethyl-n-butylamine, di-n-butylamine, or a mixture thereof. Theoxidative polymerization is initiated by the introduction of oxygen tothe reaction vessel. At the time of initiating polymerization, no morethan 10 weight percent of the total 2,6-dimethylphenol is present in thereaction mixture. Specifically, the amount of 2,6-dimethylphenolinitially present in the reaction vessel can be 1 to 10 weight percent,more specifically 1 to 5 weight percent, even more specifically 1 to 3weight percent, based on the total weight of 2,6-dimethylphenol. Theremaining 2,6-dimethylphenol, corresponding to at least 95 weightpercent of the 2,6-dimethylphenol, is added to the reaction mixtureafter the initiation of oxidative polymerization and over the course ofat least 50 minutes, specifically 50 to 80 minutes, more specifically 55to 65 minutes. During oxidative polymerization, molecular oxygen and2,6-dimethylphenol are added to the reaction mixture in a mole ratio of0.3:1 to 0.65:1, specifically 0.3:1 to 0.6:1, more specifically 0.3:1 to0.5:1. The use of the fixed ratio and the value of the ratio arebelieved to contribute significantly to the desired molecular weightproperties of final polymer product.

In some embodiments, the total weight of 2,6-dimethylphenol is 5 to 10weight percent, specifically 6 to 9 weight percent, more specifically 6to 8 weight percent, based on the total weight of 2,6-dimethylphenol andtoluene solvent.

In some embodiments, the oxidative polymerization reaction can becharacterized as comprising two stages: a first (exothermic) stageduring which the reaction vessel is cooled to maintain a desiredtemperature, and a second (“build”) phase during which the reactionvessel is heated to maintain a desired temperature. During the first(exothermic) stage, the reaction mixture can be cooled to maintain atemperature of 10 to 35° C., specifically 20 to 30° C. During the second(“build”) stage, the reaction mixture can be heated to maintain atemperature of 20 to 50° C., specifically 25 to 46° C., morespecifically 30 to 40° C.

Depending on the precise reaction conditions chosen, the totalpolymerization reaction time—that is, the time elapsed betweeninitiating oxidative polymerization and terminating oxidativepolymerization—can vary, but it is typically 120 to 250 minutes,specifically 145 to 210 minutes.

The method further comprises the step of terminating the oxidativepolymerization to form a post-termination reaction mixture. The reactionis terminated when the flow of oxygen to the reaction vessel is stopped.Residual oxygen in the reaction vessel headspace is removed by flushingwith an oxygen-free gas, such as nitrogen.

After the polymerization reaction is terminated, the copper ion of thepolymerization catalyst is separated from the reaction mixture. This isaccomplished by combining a chelant with the post-termination reactionmixture to form a chelation mixture. The chelant comprises an alkalimetal salt of nitrilotriacetic acid. In some embodiments, the chelant isa sodium or potassium salt of nitrilotriacetic acid, specificallytrisodium nitrilotriacetate. After agitation of the chelation mixture,that mixture comprises an aqueous phase comprising chelated copper ionand an organic phase comprising the dissolvedpoly(2,6-dimethyl-1,4-phenylene ether). The chelation mixture excludesthe dihydric phenol required by U.S. Pat. No. 4,110,311 to Cooper et al.The chelation mixture also excludes the aromatic amine required by U.S.Pat. No. 4,116,939 to Cooper et al. In some embodiments, the chelationmixture further excludes the mild reducing agents of U.S. Pat. No.4,110,311 to Cooper et al., which include sulfur dioxide, sulfurousacid, sodium bisulfite, sodium thionite, tin (II) chloride, iron (II)sulfate, chromium (II) sulfate, titanium (III) chloride, hydroxylaminesand salts thereof, phosphates, glucose, and mixtures thereof. Thechelation mixture is maintained at a temperature of 40 to 55° C.,specifically 45 to 50° C., for 5 to 100 minutes, specifically 10 to 60minutes, more specifically 15 to 30 minutes. The present inventors haveobserved that this combination of temperature and time is effective forcopper sequestration while also minimizing molecular weight degradationof the poly(2,6-dimethyl-1,4-phenylene ether). The chelation stepincludes (and concludes with) separating the aqueous phase and theorganic phase of the chelation mixture. This separation step isconducted at a temperature of 40 to 55° C., specifically 45 to 50° C.The time interval of 5 to 100 minutes for maintaining the chelationmixture at 40-55° C. is measured from the time at which thepost-termination reaction mixture is first combined with chelant to thetime at which separation of the aqueous and organic phases is complete.

In some embodiments, the combining a chelant with the post-terminationreaction mixture to form a chelation mixture comprises combining thepost-termination reaction mixture with an aqueous solution of thechelant, adjusting the temperature of the resulting mixture to 40 to 55°C., specifically 40 to 50° C., more specifically 45 to 50° C., andcombining the resulting temperature-adjusted mixture with water to formthe chelation mixture.

In order to reduce the elapsed time between terminating the oxidativepolymerization reaction and isolating thepoly(2,6-dimethyl-1,4-phenylene ether), it may be desirable to exclude asolvent removal step (sometimes called a “pre-concentration” step)between the terminating the oxidative polymerization and the isolatingthe poly(2,6-dimethyl-1,4-phenylene ether). As a result of suchexclusion, the separated organic phase resulting from the chelation stepcan be used directly in the isolation step. Thus, in some embodiments,isolation is conducted on a poly(2,6-dimethyl-1,4-phenylene ether)solution in which the poly(2,6-dimethyl-1,4-phenylene ether) is presentat a concentration of 5 to 10 weight percent, specifically 6 to 9 weightpercent, more specifically 6 to 8 weight percent, based on the totalweight of the poly(2,6-dimethyl-1,4-phenylene ether) solution.

In addition to polymerization and chelation steps, the method includesisolating the poly(2,6-dimethyl-1,4-phenylene ether) from the separatedorganic phase. Isolation methods that avoid exposing the separatedorganic phase to elevated temperatures—such as precipitation—arepreferred. In some embodiments, the method excludes any step, such asdevolatilizing extrusion, that exposes thepoly(2,6-dimethyl-1,4-phenylene ether) to a temperature above its glasstransition temperature. When the isolation method comprisesprecipitation, the separated organic phase is combined with anantisolvent. Suitable antisolvents include C₁-C₁₀ alkanols, C₃-C₁₀ketones, C₅-C₁₂ alkanes, and mixtures thereof. The antisolvent may,optionally, further comprise water, a C₆-C₁₂ aromatic hydrocarbon (suchas benzene, toluene, or xylene), or both.

In some embodiments, isolating the poly(2,6-dimethyl-1,4-phenyleneether) from the separated organic phase comprises mixing in a firststirred tank the separated organic phase and a first portion ofantisolvent to produce a first poly(2,6-dimethyl-1,4-phenylene ether)slurry; and mixing in a second stirred tank the firstpoly(2,6-dimethyl-1,4-phenylene ether) slurry and a second portion ofantisolvent to produce a second poly(2,6-dimethyl-1,4-phenylene ether)slurry. The separated organic phase can, optionally, comprise 6 to 10weight percent poly(2,6-dimethyl-1,4-phenylene ether). In someembodiments, the first portion of antisolvent and the second portion ofantisolvent each independently comprise 75 to 85 weight percent methanoland 15 to 25 weight percent toluene. In some embodiments, the weightratio of the separated organic phase to the first portion of antisolventis 1.5:1 to 2:1; and wherein the weight ratio of the firstpoly(2,6-dimethyl-1,4-phenylene ether) slurry to the second portion ofantisolvent is 0.9:1 to 1.2:1. In some embodiments, the mixing in afirst stirred tank and the mixing in a second stirred tank are eachindependently conducted at a temperature of 45 to 55° C. In someembodiments, the mixing in a first stirred tank and the mixing in asecond stirred tank are characterized by a total mixing energy of lessthan or equal to 4 kilojoules per kilogram, specifically 0.1 to 4kilojoules per kilogram, more specifically 0.2 to 3 kilojoules perkilogram, still more specifically 0.2 to 2 kilojoules per kilogram, evenmore specifically 0.2 to 1 kilojoule per kilogram, yet more specifically0.3 to 0.5 kilojoule per kilogram. The total mixing energy can bedetermined by measuring the energy consumption of the stirring deviceand dividing the energy consumption by the corresponding materialthroughput.

In a very specific embodiment, precipitation is performed in two stirredtanks in series. In the first stirred tank the separated organic phase(6-10 weight percent poly(2,6-dimethyl-1,4-phenylene ether)) is mixedwith a first portion of antisolvent (75-85 weight percent methanol and15-25 weight percent toluene) to produce a first slurry. In the secondtank the first slurry is mixed with an additional portion of antisolvent(75-85 weight percent methanol and 15-25 weight percent toluene). Thefirst stirred tank can have an agitator with three sets of 4-bladeturbines, 3.7 kilowatts stirring power, a residence time of about 30minutes (thus a stirring energy input of 6.7 megajoules), and a methanolconcentration of about 30%. The second stirred tank can have an agitatorwith one 4-blade turbine, 2.2 kilowatts stirring power, a residence timeof about 15 minutes (thus a stirring energy input of 2.0 megajoules),and a methanol concentration of about 55 weight percent. The first andsecond stirred tank can each be maintained at a temperature of about 50°C.

The method requires that the time elapsed between termination of theoxidative polymerization and isolating thepoly(2,6-dimethyl-1,4-phenylene ether) is no more than 200 minutes. Insome embodiments, that time is 30 to 200 minutes, specifically 30 to 100minutes, more specifically 30 to 60 minutes.

An important advantage of the method is that it produces an isolatedpoly(2,6-dimethyl-1,4-phenylene ether) solid having a number averagemolecular weight of at least 18,000 atomic mass units. In someembodiments, the number average molecular weight is 18,000 to 100,000atomic mass units, specifically 19,000 to 70,000 atomic mass units, morespecifically 20,000 to 40,000 atomic mass units, even more specifically20,000 to 35,000 atomic mass units.

In some embodiments, the isolated poly(2,6-dimethyl-1,4-phenylene ether)has a weight average molecular weight of at least 150,000 atomic massunits, specifically 150,000 to 400,000 atomic mass units, morespecifically 170,000 to 300,000 atomic mass units, still morespecifically 200,000 to 250,000 atomic mass units, yet more specifically200,000 to 230,000 atomic mass units.

Another important advantage of the method is that it produces anisolated poly(2,6-dimethyl-1,4-phenylene ether) having less than 30weight percent of molecules having a molecular weight less than 30,000atomic mass units. In some embodiments, the weight percent of moleculeshaving a molecular weight less than 30,000 atomic mass units is 10 to 30weight percent, specifically 15 to 27 weight percent, more specifically16 to 20 weight percent.

The desirable molecular weight distribution of the isolatedpoly(2,6-dimethyl-1,4-phenylene ether) is, in part, a consequence ofreducing the change in molecular weight distribution that would occur inthe chelation and pre-concentration steps of conventional processes.Thus, in some embodiments, a difference (reduction) in intrinsicviscosity less than or equal to 25 percent is observed between thedissolved poly(2,6-dimethyl-1,4-phenylene ether) and the isolatedpoly(2,6-dimethyl-1,4-phenylene ether). Specifically, the difference inintrinsic viscosity can be 10 to 25 percent, more specifically 10 to 20percent, still more specifically 11 to 15 percent. In absolute terms,the difference in intrinsic viscosity can be less than or equal to 0.30deciliters per gram between the dissolvedpoly(2,6-dimethyl-1,4-phenylene ether) and the isolatedpoly(2,6-dimethyl-1,4-phenylene ether). Values of the difference inintrinsic viscosity are presented in Table 1 in the row labeled “IV drop(%)”. For instance, Example 2 exhibits a difference in intrinsicviscosity of 100×(1.84−1.64)/1.84=11%.

Similarly, in some embodiments, a difference in weight percent ofmolecules having a molecular weight less than 30,000 atomic mass unitsless than or equal to 25 weight percent is observed between thedissolved poly(2,6-dimethyl-1,4-phenylene ether) and the isolatedpoly(2,6-dimethyl-1,4-phenylene ether). Specifically, the difference inweight percent of molecules can be 5 to 25 weight percent, morespecifically 8 to 20 weight percent, even more specifically 9 to 15weigh percent. As an illustration of this metric, consider the data forExample 2 in Table 1, below. For the dissolved (“end of reaction”)poly(2,6-dimethyl-1,4-phenylene ether), the weight percent of moleculeshaving a molecular weight less than 30,000 atomic mass units is 5.9%,and for the isolated poly(2,6-dimethyl-1,4-phenylene ether), the weightpercent of molecules having a molecular weight less than 30,000 atomicmass units is 16.2%, so the difference is 16.2%−5.9%=10.3%.

An unexpected advantage of the method is that the isolatedpoly(2,6-dimethyl-1,4-phenylene ether) has a low residual copperconcentration, even though the time and temperature of the chelationstep are reduced substantially compared to conventional commercialmethods. Thus, in some embodiments, the isolatedpoly(2,6-dimethyl-1,4-phenylene ether) has a copper concentration lessthan or equal to 5 parts per million by weight, specifically 0.1 to 5parts per million by weight, more specifically 0.5 to 5 parts permillion by weight, even more specifically 0.5 to 3 parts per million byweight, yet more specifically 1 to 3 parts per million by weight.

In some embodiments, the oxidative polymerizing comprises initiatingoxidative polymerization in the presence of 1 to 3 weight percent of the2,6-dimethylphenol; at least 97 weight percent of the 2,6-dimethylphenolis added to the reaction mixture after the initiation of oxidativepolymerization and over the course of 55 to 65 minutes; the oxidativelypolymerizing comprises adding molecular oxygen and 2,6-dimethylphenol tothe reaction mixture in a mole ratio of 0.3:1 to 0.5:1; the oxidativelypolymerizing 2,6-dimethylphenol comprises a first stage in which thereaction mixture is cooled to maintain a temperature of 20 to 30° C.,and a second stage in which the reaction mixture is heated to maintain atemperature of 30 to 40° C.; the method further comprises maintainingthe reaction mixture at a temperature of 45 to 50° C. after terminatingthe oxidative polymerization and before combining the chelant with thepost-termination reaction mixture; the method excludes a solvent removalstep between the terminating the oxidative polymerization and theisolating the poly(2,6-dimethyl-1,4-phenylene ether); the chelationmixture is maintained at a temperature of 45 to 55° C. for 40 to 70minutes; the separating the aqueous phase and the organic phase isconducted at a temperature of 45 to 55° C.; the time elapsed betweentermination of the oxidative polymerization and isolating thepoly(2,6-dimethyl-1,4-phenylene ether) is 30 to 60 minutes; the isolatedpoly(2,6-dimethyl-1,4-phenylene ether) has a number average molecularweight of 20,000 to 35,000 atomic mass units and 16 to 20 weight percentof molecules having a molecular weight less than 30,000 atomic massunits; and the isolated poly(2,6-dimethyl-1,4-phenylene ether) has acopper concentration of 0.5 to 5 parts per million by weight.

One embodiment is a poly(2,6-dimethyl-1,4-phenylene ether) solid havinga number average molecular weight of at least 18,000 atomic mass units,and less than 30 weight percent of molecules having a molecular weightless than 30,000 atomic mass units. Specifically the number averagemolecular weight can be 18,000 to 100,000 atomic mass units, morespecifically 19,000 to 70,000 atomic mass units, still more specifically20,000 to 40,000 atomic mass units, yet more specifically 20,000 to35,000 atomic mass units. And the weight percent of molecules having amolecular weight less than 30,000 atomic mass units can be,specifically, 10 to 30 weight percent, more specifically 15 to 27 weightpercent, still more specifically 16 to 20 weight percent. In someembodiments, the poly(2,6-dimethyl-1,4-phenylene ether) solid has acopper concentration less than or equal to 5 parts per million byweight, specifically 0.1 to 5 parts per million by weight, morespecifically 0.5 to 5 parts per million by weight, even morespecifically 0.5 to 3 parts per million by weight, yet more specifically1 to 3 parts per million by weight.

One embodiment is a poly(2,6-dimethyl-1,4-phenylene ether) solid havinga number average molecular weight of 20,000 to 35,000 atomic mass units,16 to 20 weight percent of molecules having a molecular weight less than30,000 atomic mass units, and a copper concentration of 0.5 to 5 partsper million by weight.

The poly(2,6-dimethyl-1,4-phenylene ether) solid is particularly usefulfor forming fibers, especially hollow fibers for use in asymmetrichollow fiber membranes. Techniques for preparing asymmetric hollow fibermembranes comprising polyphenylene ethers are known in the art anddescribed in, for example, J. Smid, J. H. M. Albers, and A. P. M.Kusters, Journal of Membrane Science, volume 64, pages 121-128 (1991),and U.S. Pat. Nos. 3,852,388 to Kimura, 4,486,202 to Malon et al.,4,944,775 to Hayes, 5,181,940 to Bikson, 5,215,554 to Kramer et al., and7,229,580 to Yuan. Another embodiment is a fluid separation apparatuscomprising an asymmetric hollow fiber membrane comprising thepoly(2,6-dimethyl-1,4-phenylene ether) solid. For example, the fluidseparation apparatus can be used to separate oxygen from air. Techniquesfor constructing fluid separation apparatuses comprising asymmetrichollow fiber membranes are known in the art and described in, forexample, U.S. Pat. Nos. 5,679,133 to Moll et al., and 5,779,897 toKalthod et al.

The poly(2,6-dimethyl-1,4-phenylene ether) is also useful for formingother articles, such as pipes, conduits, and other extruded profiles foruse in construction of building interiors. The compositions used to formsuch article may comprise, in addition to thepoly(2,6-dimethyl-1,4-phenylene ether), a poly(alkenyl aromatic), apolyolefin, a polyamide, a polyester, or a combination thereof, as wellas various additives known in the thermoplastic arts. Articles can beprepared using fabrication methods known in the art, including, forexample, single layer and multilayer foam extrusion, single layer andmultilayer sheet extrusion, injection molding, blow molding, extrusion,film extrusion, profile extrusion, pultrusion, compression molding,thermoforming, pressure forming, hydroforming, vacuum forming, foammolding, and the like. Combinations of the foregoing article fabricationmethods can be used.

The invention includes at least the following embodiments.

Embodiment 1

A method of preparing a poly(2,6-dimethyl-1,4-phenylene ether),comprising: oxidatively polymerizing 2,6-dimethylphenol in toluenesolvent in the presence of a catalyst comprising copper ion andN,N′-di-tert-butylethylenediamine to form a reaction mixture comprisinga dissolved poly(2,6-dimethyl-1,4-phenylene ether), water, and thecatalyst; wherein the oxidative polymerizing comprises initiatingoxidative polymerization in the presence of no more than 10 weightpercent of the 2,6-dimethylphenol; wherein at least 95 weight percent ofthe 2,6-dimethylphenol is added to the reaction mixture after theinitiation of oxidative polymerization and over the course of at least50 minutes; wherein the oxidatively polymerizing comprises addingmolecular oxygen and 2,6-dimethylphenol to the reaction mixture in amole ratio of 0.3:1 to 0.65:1; terminating the oxidative polymerizationto form a post-termination reaction mixture; combining a chelantcomprising an alkali metal salt of nitrilotriacetic acid with thepost-termination reaction mixture to form a chelation mixture comprisingan aqueous phase comprising chelated copper ion, and an organic phasecomprising the dissolved poly(2,6-dimethyl-1,4-phenylene ether); whereinthe chelation mixture excludes dihydric phenols and aromatic amines;maintaining the chelation mixture at a temperature of 40 to 55° C. for 5to 100 minutes; separating the aqueous phase and the organic phase;wherein the separation is conducted at a temperature of 40 to 55° C.;and isolating the poly(2,6-dimethyl-1,4-phenylene ether) from theseparated organic phase; wherein time elapsed between termination of theoxidative polymerization and isolating thepoly(2,6-dimethyl-1,4-phenylene ether) is no more than 200 minutes; andwherein the isolated poly(2,6-dimethyl-1,4-phenylene ether) has a numberaverage molecular weight of at least 18,000 atomic mass units and lessthan 30 weight percent of molecules having a molecular weight less than30,000 atomic mass units.

Embodiment 2

The method of embodiment 1, wherein the chelation mixture furtherexcludes mild reducing agents selected from the group consisting ofsulfur dioxide, sulfurous acid, sodium bisulfite, sodium thionite, tin(II) chloride, iron (II) sulfate, chromium (II) sulfate, titanium (III)chloride, hydroxylamines and salts thereof, phosphates, glucose, andmixtures thereof.

Embodiment 3

The method of embodiment 1 or 2, wherein the oxidatively polymerizing2,6-dimethylphenol comprises a first stage in which the reaction mixtureis cooled to maintain a temperature of 10 to 35° C.

Embodiment 4

The method of embodiment 3, wherein the oxidatively polymerizing2,6-dimethylphenol comprises a second stage in which the reactionmixture is heated to maintain a temperature of 20 to 50° C.

Embodiment 5

The method of any of embodiments 1-4, wherein the total weight of2,6-dimethylphenol is 5 to 10 weight percent based on the total weightof 2,6-dimethylphenol and toluene solvent.

Embodiment 6

The method of any of embodiments 1-5, wherein the combining a chelantwith the post-termination reaction mixture to form a chelation mixturecomprises combining the post-termination reaction mixture with anaqueous solution of the chelant, adjusting the temperature of theresulting mixture to 40 to 55° C., and combining the resultingtemperature-adjusted mixture with water to form the chelation mixture.

Embodiment 7

The method of any of embodiments 1-6, excluding a solvent removal stepbetween the terminating the oxidative polymerization and the isolatingthe poly(2,6-dimethyl-1,4-phenylene ether).

Embodiment 8

The method of any of embodiments 1-7, wherein the isolating thepoly(2,6-dimethyl-1,4-phenylene ether) from the separated organic phasecomprises mixing in a first stirred tank the separated organic phase anda first portion of antisolvent to produce a firstpoly(2,6-dimethyl-1,4-phenylene ether) slurry; and mixing in a secondstirred tank the first poly(2,6-dimethyl-1,4-phenylene ether) slurry anda second portion of antisolvent to produce a secondpoly(2,6-dimethyl-1,4-phenylene ether) slurry.

Embodiment 9

The method of embodiment 8, wherein the separated organic phasecomprises 6 to 10 weight percent poly(2,6-dimethyl-1,4-phenylene ether).

Embodiment 10

The method of embodiment 8 or 9, wherein the first portion ofantisolvent and the second portion of antisolvent each independentlycomprise 75 to 85 weight percent methanol and 15 to 25 weight percenttoluene.

Embodiment 11

The method of any of embodiments 8-10, wherein the weight ratio of theseparated organic phase to the first portion of antisolvent is 1.5:1 to2:1; and wherein the weight ratio of the firstpoly(2,6-dimethyl-1,4-phenylene ether) slurry to the second portion ofantisolvent is 0.9:1 to 1.2:1.

Embodiment 12

The method of any of embodiments 8-11, wherein the mixing in a firststirred tank and the mixing in a second stirred tank are eachindependently conducted at a temperature of 45 to 55° C.

Embodiment 13

The method of any of embodiments 8-12, wherein the mixing in a firststirred tank and the mixing in a second stirred tank are characterizedby a total mixing energy of less than or equal to 4 kilojoules perkilogram.

Embodiment 14

The method of any of embodiments 1-13, wherein the isolatedpoly(2,6-dimethyl-1,4-phenylene ether) has a weight average molecularweight of at least 150,000 atomic mass units.

Embodiment 15

The method of any of embodiments 1-14, wherein the isolatedpoly(2,6-dimethyl-1,4-phenylene ether) has a weight average molecularweight of 150,000 to 230,000 atomic mass units.

Embodiment 16

The method of any of embodiments 1-15, wherein a difference in intrinsicviscosity less than or equal to 25 percent is observed between thedissolved poly(2,6-dimethyl-1,4-phenylene ether) and the isolatedpoly(2,6-dimethyl-1,4-phenylene ether).

Embodiment 17

The method of any of embodiments 1-16, wherein a difference in intrinsicviscosity of 10 to 25 percent is observed between the dissolvedpoly(2,6-dimethyl-1,4-phenylene ether) and the isolatedpoly(2,6-dimethyl-1,4-phenylene ether).

Embodiment 18

The method of any of embodiments 1-17, wherein a difference in intrinsicviscosity less than or equal to 0.30 deciliters per gram is observedbetween the dissolved poly(2,6-dimethyl-1,4-phenylene ether) and theisolated poly(2,6-dimethyl-1,4-phenylene ether).

Embodiment 19

The method of any of embodiments 1-18, wherein a difference in weightpercent of molecules having a molecular weight less than 30,000 atomicmass units of less than or equal to 25 weight percent is observedbetween the dissolved poly(2,6-dimethyl-1,4-phenylene ether) and theisolated poly(2,6-dimethyl-1,4-phenylene ether).

Embodiment 20

The method of any of embodiments 1-19, wherein a difference in weightpercent of molecules having a molecular weight less than 30,000 atomicmass units of 10 to 25 weight percent is observed between the dissolvedpoly(2,6-dimethyl-1,4-phenylene ether) and the isolatedpoly(2,6-dimethyl-1,4-phenylene ether).

Embodiment 21

The method of any of embodiments 1-20, wherein the isolatedpoly(2,6-dimethyl-1,4-phenylene ether) has a copper concentration lessthan or equal to 5 parts per million by weight.

Embodiment 22

The method of any of embodiments 1-21, wherein the isolatedpoly(2,6-dimethyl-1,4-phenylene ether) has a copper concentration of 0.5to 5 parts per million by weight.

Embodiment 23

The method of any of embodiments 1-22, wherein the catalyst furthercomprises dimethyl-n-butylamine, di-n-butylamine, or a mixture thereof.

Embodiment 24

The method of any of embodiments 1-23, wherein the catalyst furthercomprises dimethyl-n-butylamine and di-n-butylamine.

Embodiment 25

The method of embodiment 1, wherein the catalyst further comprisesdimethyl-n-butylamine and di-n-butylamine; wherein the oxidativepolymerizing comprises initiating oxidative polymerization in thepresence of 1 to 3 weight percent of the 2,6-dimethylphenol; wherein atleast 97 weight percent of the 2,6-dimethylphenol is added to thereaction mixture after the initiation of oxidative polymerization andover the course of 55 to 65 minutes; wherein the oxidativelypolymerizing comprises adding molecular oxygen and 2,6-dimethylphenol tothe reaction mixture in a mole ratio of 0.3:1 to 0.5:1; wherein theoxidatively polymerizing 2,6-dimethylphenol comprises a first stage inwhich the reaction mixture is cooled to maintain a temperature of 20 to30° C., and a second stage in which the reaction mixture is heated tomaintain a temperature of 30 to 40° C.; wherein the method excludes asolvent removal step between the terminating the oxidativepolymerization and the isolating the poly(2,6-dimethyl-1,4-phenyleneether); wherein the chelation mixture is maintained at a temperature of45 to 55° C. for 40 to 70 minutes; wherein the separating the aqueousphase and the organic phase is conducted at a temperature of 45 to 55°C.; wherein time elapsed between termination of the oxidativepolymerization and isolating the poly(2,6-dimethyl-1,4-phenylene ether)is 30 to 60 minutes; wherein the isolatedpoly(2,6-dimethyl-1,4-phenylene ether) has a number average molecularweight of 20,000 to 35,000 atomic mass units and 16 to 20 weight percentof molecules having a molecular weight less than 30,000 atomic massunits; and wherein the isolated poly(2,6-dimethyl-1,4-phenylene ether)has a copper concentration of 0.5 to 5 parts per million by weight.

Embodiment 26

A poly(2,6-dimethyl-1,4-phenylene ether) made by the method of any ofembodiments 1-25.

Embodiment 27

A fiber comprising the poly(2,6-dimethyl-1,4-phenylene ether) solid ofembodiment 26.

Embodiment 28

An article comprising the poly(2,6-dimethyl-1,4-phenylene ether) solidof embodiment 26.

Embodiment 29

A poly(2,6-dimethyl-1,4-phenylene ether) solid having a number averagemolecular weight of at least 18,000 atomic mass units, and less than 30weight percent of molecules having a molecular weight less than 30,000atomic mass units.

Embodiment 30

The poly(2,6-dimethyl-1,4-phenylene ether) solid of embodiment 29,having a copper concentration less than or equal to 5 parts per millionby weight.

Embodiment 31

The poly(2,6-dimethyl-1,4-phenylene ether) solid of embodiment 29 or 30,having a number average molecular weight of 20,000 to 35,000 atomic massunits, 16 to 20 weight percent of molecules having a molecular weightless than 30,000 atomic mass units, and a copper concentration of 0.5 to5 parts per million by weight.

Embodiment 32

A fiber comprising the poly(2,6-dimethyl-1,4-phenylene ether) solid ofany of embodiments 29-31.

Embodiment 33

An article comprising the poly(2,6-dimethyl-1,4-phenylene ether) solidof any of embodiments 29-31.

Embodiment 34

The article of embodiment 33, wherein the article is an asymmetrichollow fiber membrane.

Embodiment 35

A fluid separation apparatus comprising the asymmetric hollow fibermembrane of embodiment 34.

The invention is further illustrated by the following non-limitingexamples.

Examples 1-2, Comparative Examples 1-3

These examples illustrate variations in poly(2,6-dimethyl-1,4-phenyleneether) process variables including the percentage of total2,6-dimethylphenol present in the reaction mixture when thepolymerization is initiated, the time over which the remainder of the2,6-dimethylphenol is added to the reaction mixture, the molar ratio of2,6-dimethylphenol to catalyst metal in the reaction mixture, the molarratio of oxygen to 2,6-dimethylphenol fed to the reaction mixture, thereaction mixture temperatures during the build and pump-out stages, thetotal reaction time, the time between termination of the polymerizationreaction and the start of precipitation, and the time betweentermination of the polymerization reaction and the completion ofprecipitation.

The general reaction procedure was as follows. A percentage of the total2,6-dimethylphenol (which has a purity of 99.86%), as specified in Table1, is dissolved in toluene in a reaction vessel. To the resulting2,6-dimethylphenol solution is added cuprous oxide in 48 weight percentHBr aqueous solution (a solution that is 6.5 weight percent copper),N,N′-dibutylethylenediamine (DBEDA; added as an approximately 25-28weight percent solution in toluene), dimethylbutylamine (DMBA),di-n-butylamine (DBA), and didecyl dimethyl ammonium chloride. The molarratio of total 2,6-dimethyl phenol to copper is specified in Table 1, asis the molar ratio of DBEDA to copper. The reaction is conducted as asemi-batch process with the continuous addition of 2,6-dimethylphenolover a period of time, and oxygen is added at a fixed rate (specified inTable 1) relative to the rate of 2,6-dimethylphenol addition. (Thisfixed rate of oxygen addition is maintained until the reaction nearscompletion, as evidenced by a step increase in headspace oxygenconcentration; at that point, the rate of oxygen addition is decreasedto maintain a headspace oxygen concentration no greater than 17 volumepercent.) The time of “initiating oxidative polymerization” is the timeat which oxygen is first introduced to the reaction mixture. Allreaction mixtures had total solids of 7.1 weight percent, where totalsolids is the weight percent of total 2,6-dimethylphenol relative to thesum of total 2,6-dimethylphenol and toluene solvent. The initial phaseof the reaction is exothermic, and cooling is used to maintain areaction mixture temperature of about 30° C. When the exothermic phaseof the reaction is completed, the so-called “build” phase of thereaction begins, and heating is used to raise the reaction mixturetemperature to the value specified in Table 1. The end point of thereaction is reached at a fixed reaction time, e.g., 130 minutes, whenthe in-line viscosity reading indicates no further molecular weightbuild is occurring. At this point, flow of oxygen to the reactor isceased (which terminates the polymerization reaction), oxygen in theheadspace is removed (flushed out), an aqueous solution of the chelanttrisodium nitrilotriacetate (Na₃NTA) is added to the reactor, and thetemperature of the resulting mixture is adjusted to the so-called“pump-out” temperature. At this time, a small sample of the reactionmixture is removed. The small sample of the reaction mixture is dilutedand analyzed by gel permeation chromatography to determine its intrinsicviscosity (“end of reaction IV”). The end of reaction intrinsicviscosity is determined using gel permeation chromatography as describedbelow, using as calibration standards differentpoly(2,6-dimethyl-1,4-phenylene ether) samples having known intrinsicviscosities previously measured by Ubbelohde in chloroform at 25° C.

The reaction mixture is then pumped out of the reaction vessel into avessel containing additional water. The resulting mixture is mixed for aspecified time, then separated via liquid-liquid centrifugation to yielda poly(2,6-dimethyl-1,4-phenylene ether) solution and an aqueous phase.The poly(2,6-dimethyl-1,4-phenylene ether) solution thus obtained iscombined with antisolvent to precipitate thepoly(2,6-dimethyl-1,4-phenylene ether) as a powder. Typicalprecipitation conditions include using a poly(2,6-dimethyl-1,4-phenyleneether) solution with a poly(2,6-dimethyl-1,4-phenylene ether)concentration of 5-10 weight percent, a weight ratio of antisolvent topoly(2,6-dimethyl-1,4-phenylene ether) solution of 0.5:1 to 0.6:1 in afirst precipitation tank and 1.7:1 to 2:1 in a second precipitationtank. The precipitated poly(2,6-dimethyl-1,4-phenylene ether) powder isisolated via filtration followed by two cycles of slurrying the powderwith antisolvent and separating the powder with solid/liquidcentrifugation. The start of precipitation is the time when a firstportion of the poly(2,6-dimethyl-1,4-phenylene ether) solution iscombined with a first portion of the antisolvent. The end ofprecipitation is the time when the last portion of thepoly(2,6-dimethyl-1,4-phenylene ether) solution is combined with thelast portion of antisolvent. The time elapsed between the end ofreaction and start of precipitation is noted, as is the time elapsedbetween the end of reaction and the end of precipitation. The isolatedpoly(2,6-dimethyl-1,4-phenylene ether) powder is dried for 60-90 minutesat 180° C. and atmospheric pressure, using steam and nitrogen to flushaway the toluene vapors. The intrinsic viscosity of the isolated powder(“powder IV”) was measured by dissolving a sample of the isolated powderin toluene and analyzing by gel permeation chromatography as describedfor the dissolved (“end of reaction”) sample.

Number average molecular weight and weight average molecular weight weredetermined by gel permeation chromatography as follows. The gelpermeation chromatograph is calibrated using eight polystyrenestandards, each of narrow molecular weight, and collectively spanning amolecular weight range of 3,000 to 1,000,000 grams/mole. The columnsused were 1e3 and 1e5 angstrom Plgel columns with a 5 microliter 100angstrom PLgel guard column. Chromatography was conducted at 25° C. Theelution liquid was chloroform with 100 parts per million by weightdi-n-butylamine The elution flow was 1.2 milliliters per minute. Thedetector wavelengths were 254 nanometers (for polystyrene standards) and280 nanometers (for poly(2,6-dimethyl-1,4-phenylene ether)). A thirddegree polynomial function is fitted through the calibration points.Poly(2,6-dimethyl-1,4-phenylene ether) samples are prepared bydissolving 0.27 grams poly(2,6-dimethyl-1,4-phenylene ether) solid in 45milliliters toluene. A 50 microliter sample of the resulting solution isinjected into the chromatograph. The values of number average molecularweight (M_(n)) and weight average molecular weight (M_(w)) arecalculated from the measured signal using the polystyrene calibrationline. The values are subsequently converted from polystyrene molecularweight to true poly(2,6-dimethyl-1,4-phenylene ether) molecular weightsusing the formula: M(PPO)=0.3122×M(PS)^(1.073).

Process variations are summarized in Table 1. In Table 1, “Initial2,6-dimethylphenol (wt %)” is the weight percent of total2,6-dimethylphenol initially present in the reaction mixture; “Additiontime (min)” is the time in minutes over which the remainder of2,6-dimethylphenol is added; “2,6-dimethylphenol:Cu mole ratio” is themolar ratio of total 2,6-dimethylphenol to copper; “DBEDA:Cu mole ratio”is the molar ratio of N,N′-di-tert-butylethylenediamine to copper;“Oxygen:2,6-dimethylphenol feed mole ratio” is the molar ratio ofmolecular oxygen to 2,6-dimethylphenol fed to the reaction mixtureduring the addition of the remainder of 2,6-dimethylphenol; “Buildtemperature (° C.)” is the temperature in degrees centigrade at whichthe reaction mixture is maintained during the build phase of thereaction; “Total reaction time (min)” is the elapsed time in minutesbetween the beginning of the polymerization reaction (introduction ofoxygen to the reaction vessel) and the end of the polymerizationreaction (termination of oxygen addition to the reaction vessel);“Pump-out temperature (° C.)” is the temperature in degrees centigradeto which the combined reaction mixture and chelant solution are raisedbefore being pumped out of the reactor into a vessel with additionalwater; “Total chelation time (min)” is the elapsed time betweeninitiating addition of the chelant solution to the post-terminationreaction mixture and completing separation of the combined reactionmixture, chelant solution, and additional water into apoly(2,6-dimethyl-1,4-phenylene ether) solution and an aqueous phase;“Time to start precipitation (min)” is the elapsed time in minutesbetween the end of the polymerization reaction and the time when a firstportion of the poly(2,6-dimethyl-1,4-phenylene ether) solution iscombined with a first portion of the antisolvent; “Time to end ofprecipitation (min)” is the elapsed time in minutes between the end ofprecipitation and the time when the last portion of thepoly(2,6-dimethyl-1,4-phenylene ether) solution is combined with thelast portion of antisolvent; “End of reaction IV (dL/g)” is theintrinsic viscosity, expressed in deciliters per gram, of thepoly(2,6-dimethyl-1,4-phenylene ether) at the end of the polymerizationreaction; “Powder IV (dL/g)” is the intrinsic viscosity, expressed indeciliters per gram, of the finally isolatedpoly(2,6-dimethyl-1,4-phenylene ether) powder (i.e., the product of thecomplete process); “IV drop (%)” is the percentage change in intrinsicviscosity between the end of the polymerization reaction and the finalisolation; “End of reaction M_(n) (AMU)” is the number average molecularweight, expressed in atomic mass units (AMU), of thepoly(2,6-dimethyl-1,4-phenylene ether) at the end of the polymerizationreaction; “Isolated powder M_(n) (AMU)” is the number average molecularweight, expressed in atomic mass units, of the finally isolatedpoly(2,6-dimethyl-1,4-phenylene ether) powder; “End of reactionM_(w)/M_(n)” is the polydispersity index (weight average molecularweight divided by number average molecular weight) of thepoly(2,6-dimethyl-1,4-phenylene ether) at the end of the polymerizationreaction; “Isolated powder M_(w)/M_(n)” is the polydispersity index(weight average molecular weight divided by number average molecularweight) of the isolated poly(2,6-dimethyl-1,4-phenylene ether) powder;“End of reaction wt %<30,000(%)” is the weight percent of theend-of-reaction poly(2,6-dimethyl-1,4-phenylene ether) having amolecular weight less than 30,000 atomic mass units; “Isolated powder wt%<30,000(%)” is the weight percent of the finally isolatedpoly(2,6-dimethyl-1,4-phenylene ether) having a molecular weight lessthan 30,000 atomic mass units.

The results in Table 1 show that Examples 1 and 2 exhibited much smallerreductions in intrinsic viscosity and much smaller increases in weightfraction less than 30,000 atomic mass units between end of reaction andisolation than did Comparative Examples 1-3. Examples 1 and 2 had lowerpump-out temperatures and shorter elapsed times between end of reactionand precipitation than did the Comparative Examples.

TABLE 1 C. Ex. 1 C. Ex. 2 C. Ex. 3 Ex. 1 Ex. 2 Initial2,6-dimethylphenol (wt %) 10 10 10 2.5 2.5 Addition time (min) 45 45 4558 58 2,6-dimethylphenol:Cu mole  114:1  108:1  108:1  101:1  101:1ratio DBEDA:Cu mole ratio 1.83 1.74 1.74 1.74 1.78Oxygen:2,6-dimethylphenol 0.39:1 0.39:1 0.39:1 0.57:1 0.57:1 feed moleratio Build temperature (° C.) 46 46 46 46 40 Total reaction time (min)130 130 130 145 207 Pump-out temperature (° C.) 60 60 60 50 50 Totalchelation time (min) 80 80 80 <30 <30 Time to start of precipitation 650420 360 200 60 (min) Time to end of precipitation 800 580 540 410 240(min) End of reaction IV (dL/g) 1.68 2.05 2.05 1.91 1.84 Isolated powderIV (dL/g) 1.05 1.42 1.37 1.55 1.64 IV drop (%) 38 31 33 21 11 End ofreaction M_(n) (AMU) 88,000 — — 93,000 75,000 Isolated powder M_(n)(AMU) 14,000 — — 19,000 33,000 Isolated powder M_(w) (AMU) 133,000 — —209,000 228,000 End of reaction M_(w)/M_(n) 2.5 — — 2.9 3.4 Isolatedpowder M_(w)/M_(n) 9.5 — — 11.0 6.9 End of reaction wt % <30,000 5.2 — —5.0 5.9 (%) Isolated powder wt % <30,000 42.1 — — 26.4 16.2 (%)

Comparative Examples 4-18

These experiments were conducted on a laboratory scale and are intendedto isolate the effects of individual process variables. All reactionmixtures included 270 grams of 2,6-dimethylphenol and 3,200 grams oftoluene. The addition time for 2,6-dimethylphenol was always 45 minutes.During the build phase of the reaction, oxygen concentration wasmaintained at 10 volume percent. After 130 minutes of reaction (at theend of the build phase), oxygen flow to the reactor was stopped. Then,the temperature of the reaction mixture was increased to 60° C. and atrisodium nitrilotriacetate solution was added to chelate the coppercatalyst. After 90 minutes of stirring at 60° C., the mixture wascentrifuged for 50 minutes at 70° C. to separate the aqueous and organicphases. The poly(2,6-dimethyl-1,4-phenylene ether) was precipitated bycombining the organic phase with methanol antisolvent, and the resultingpoly(2,6-dimethyl-1,4-phenylene ether) powder was filtered and driedovernight at 135° C.

In Table 2, “Catalyst (g)” refers to the weight, in grams, of thecuprous oxide solution described above; “DBEDA (g)” refers to theweight, in grams, of N,N′-dibutylethylenediamine; “DBA (g)” refers tothe weight, in grams, of di-n-butylamine; “DMBA (g)” refers to theweight, in grams of dimethyl-n-butylamine; “Oxygen flow (SLM)” refers tothe oxygen flow rate, in standard liters per minute, into the reactionvessel during the exotherm phase of the reaction; “Exotherm temperature(° C.)” is the temperature at which the reaction mixture is maintained(via cooling) during the exotherm phase of the reaction; “Isolatedpowder M_(w)/M_(n)” is the polydispersity index (weight averagemolecular weight divided by number average molecular weight) of theisolated poly(2,6-dimethyl-1,4-phenylene ether) powder.

Analysis of the results for the group of examples summarized in thefirst part of Table 2 reveals that higher end-of-reaction intrinsicviscosities are associated with lower oxygen flow rates and lowertemperatures during the exotherm phase. Analysis of the group ofexamples summarized in the second part (the first continuation) of Table2 reveals that higher end-of-reaction intrinsic viscosities areassociated with higher catalyst concentrations. Analysis of the group ofexamples summarized in the third part (the second continuation) of Table2 revealed no statistically significant correlation betweenend-of-reaction intrinsic viscosities and di-n-butylamine concentration.

TABLE 2 C. C. C. C. C. C. C. Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10Catalyst (g) 27.3 34.1 27.3 27.3 27.3 27.3 27.3 DBEDA (g) 8.4 10.5 8.48.4 8.4 8.4 8.4 DBA (g) 11 11 11 11 11 11 11 DMBA (g) 87 87 115 87 87 8787 Initial 10 10 10 10 0 10 10 2,6-dimethylphenol (wt %) Oxygen flow(SLM) 0.66 0.66 0.66 0.66 0.40 0.40 0.66 Exotherm 25 25 25 10 25 25 25temperature (° C.) End of reaction IV 1.58 1.65 1.67 2.05 1.92 1.98 1.34(dL/g) Isolated powder IV 1.60 1.68 1.69 1.92 1.87 1.61 1.36 (dL/g)Isolated powder 3.3 3.9 4.0 4.4 4.3 7.1 3.7 M_(w)/M_(n) C. Ex. 11 C. Ex.12 C. Ex. 13 C. Ex. 14 Catalyst (g) 21.9 14.6 21.9 14.6 DBEDA (g) 6.74.5 6.7 4.5 DBA (g) 11 11 11 11 DMBA (g) 87 87 87 87 Initial 10 10 10 102,6-dimethylphenol (wt %) Oxygen flow (SLM) 0.53 0.40 0.40 0.53 Exothermtemperature 15 15 15 15 (° C.) End of reaction IV 2.15 1.78 2.18 1.72(dL/g) Isolated powder IV 1.93 1.25 1.70 1.31 (dL/g) Isolated powder 5.06.1 6.4 5.3 M_(w)/M_(n) C. Ex. 15 C. Ex. 16 C. Ex. 17 C. Ex. 18 Catalyst(g) 42.3 29.6 29.6 29.6 DBEDA (g) 13.0 9.1 9.1 9.2 DBA (g) 0 0 2.8 5.5DMBA (g) 87 87 87 87 Initial 10 10 10 10 2,6-dimethylphenol (wt %)Oxygen flow (SLM) 0.40 0.40 0.40 0.40 Exotherm temperature 25 25 25 25(° C.) End of reaction IV 2.48 2.03 1.82 2.11 (dL/g) Isolated powder IV2.73 2.12 1.78 2.00 (dL/g) Isolated powder 5.8 4.5 5.6 5.5 M_(w)/M_(n)

Comparative Examples 19-32

These examples illustrate the effects of chelation temperature and timeon the intrinsic viscosity of a poly(2,6-dimethyl-1,4-phenylene ether).The poly(2,6-dimethyl-1,4-phenylene ether) was produced in a lab-scalereactor using 17.3 grams catalyst, 5.33 grams di-t-butylethylenediamine,9.86 gram di-n-butylamine, 32.1 gram dimethyl-n-butylamine, 5 weightpercent of total 2,6-dimethylphenol initially present, an oxygen flow of0.30 standard liters per minute, and a 30° C. exotherm temperature.After stopping the oxygen feed, the resulting solution was divided intotwo jacketed vessels and trisodium nitrilotriacetate and water wereadded. One vessel was kept at 50° C. and the other at 60° C. At thenoted times, a sample was taken from the vessels and (after dilutionwith toluene) injected into a gel permeation chromatograph to determinethe intrinsic viscosity of the poly(2,6-dimethyl-1,4-phenylene ether).The results, presented in Table 3, show that thepoly(2,6-dimethyl-1,4-phenylene ether) intrinsic viscosity drops at arate of about 5% per hour when the chelation temperature is 50° C., anda rate of about 11% per hour when the chelation temperature is 60° C.

TABLE 3 Chelation Chelation Intrinsic Intrinsic temperature timeviscosity viscosity (° C.) (hours) (dL/g) change (%) M_(w)/M_(n) C. Ex.19 50 0 1.755 0 2.80 C. Ex. 20 50 1 1.721 2 2.65 C. Ex. 21 50 2 1.656 63.29 C. Ex. 22 50 3 1.555 11 3.54 C. Ex. 23 50 4 1.431 18 3.88 C. Ex. 2450 20 0.641 63 5.03 C. Ex. 25 50 24 0.607 65 5.14 C. Ex. 26 60 0 1.755 02.80 C. Ex. 27 60 1 1.616 8 3.66 C. Ex. 28 60 2 1.349 23 4.86 C. Ex. 2960 3 1.153 34 5.64 C. Ex. 30 60 4 0.996 43 6.18 C. Ex. 31 60 20 0.552 695.45 C. Ex. 32 60 24 0.531 70 5.73

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the claims, and may include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral language of the claims.

All cited patents, patent applications, and other references areincorporated herein by reference in their entirety. However, if a termin the present application contradicts or conflicts with a term in theincorporated reference, the term from the present application takesprecedence over the conflicting term from the incorporated reference.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are independently combinable with each other.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Further, it should further be noted that the terms “first,”“second,” and the like herein do not denote any order, quantity, orimportance, but rather are used to distinguish one element from another.The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (e.g., itincludes the degree of error associated with measurement of theparticular quantity).

1. A poly(2,6-dimethyl-1,4-phenylene ether) solid having a numberaverage molecular weight of at least 18,000 atomic mass units, and lessthan 30 weight percent of molecules having a molecular weight less than30,000 atomic mass units.
 2. The poly(2,6-dimethyl-1,4-phenylene ether)solid of claim 1, having a copper concentration less than or equal to 5parts per million by weight.
 3. The poly(2,6-dimethyl-1,4-phenyleneether) solid of claim 1, having a number average molecular weight of20,000 to 35,000 atomic mass units, 16 to 20 weight percent of moleculeshaving a molecular weight less than 30,000 atomic mass units, and acopper concentration of 0.5 to 5 parts per million by weight.
 4. A fibercomprising the poly(2,6-dimethyl-1,4-phenylene ether) solid of claim 1.5. An article comprising the poly(2,6-dimethyl-1,4-phenylene ether)solid of claim
 1. 6. The article of claim 5, wherein the article is anasymmetric hollow fiber membrane.